Chemical production of oxygen



June 3, 1 G. JENNESS CHEMICAL PRODUCTION OF OXYGEN Filed July 3. 1942 M Sw l 5T A. l` w ',Patented June 3, 1947 ATENT OFFICE CHEBHCAL PRDUCTION F OXYGEN Leslie G. Jenness, Bualo, N. Y., assignor to The Linde Air Products Company, a corporation of Ohio Application `uly 3, 1942, Serial No. 449,687

8 Claims.

This invention relates to a novel chemical process for extracting oxygen from a mixture of oxygen with inert gas, 4and particularly for separating `and collecting gaseous oxygen of high purity from the atmosphere'. More particularly, the invention relates to an improvement on the basic process of Du Motay and Marechal disclosed in United States Patent 70,705 of November 12, 1867. The invention is also concerned with a novel process for reactivating a contact mass which has become exhausted during its use in the process for producing oxygen.

The process of Du Motay et al. is performed by alternately passing air and steam through a closed retort over a hot alkali manganate or similar reaction mass having the ability to b'e oxidized by the passage of air thereover, and thereafter to be deoxidized and release the gaseous oxygen during the passage of steam thereover. The reversible reaction theoretically is:

Steam Various reaction masses may be used in the process, as disclosed by Du Motay et al., including the manganates and permanganates of potassium, sodium, or barium, as Well as the chromates and ferrates of these metals, and ln general all metallic acids or oxides forming, with potassium, sodium, or barium, binary combinations capable of becoming super-oxidized, and also possessing the property of releasing their oxygen at a temperature more or less elevated when they are placed in the presence of a current of steam. During the passage of steam over the hot mass, the gaseous oxygen is collected while the residual steam is condensed and separated from the oxygen. Oxygen of 95% purity or better may be obtained by this process. Of course the nitrogen residue from the air phase of the cycle also may be collected, if this is desired.

The basic process of Du Motay et al. has not been commercially successful in competition with other methods of producing oxygen because of several disadvantages rendering the process economically unprotable. One of the principal drawbacks of the Du Motay et al. process is the instability of the reaction mass, which deteriorates rapidly after being in service only a short time, with a resulting low oxygen production based on the quantities of air and steam passed over the mass. Moreover, the process Would consume huge quantities of steam for the production of oxygen on a large scale, thus making the cost of operation prohibitive. Another serious disadtion. Among the best known of these improve.

ments was proposed by George Kaszner in United States Pat/ent 1,015,566, of January 23,V 1912, which teaches the addition to the alkali manganate mass of an alkali meta-plumbate, such as sodium meta-plumbate, for increased stability. Despite the alleged improvement in the stability of the reaction mass, however, there is no substantial increase in the eiciency of oxygen production based on the quantities of steam and air supplied to the mass. Thus, the cost of operation by Kaszners process is prohibitive in competition with other commercial processes for producing oxygen.

The principal object of the present invention is to provide a novel chemical process for extracting oxygen from a mixture of oxygen with'inert gas, and particularly for producing oxygen from the air without the disadvantages of the prior processes discussed above. Another object is the provision of a novel process for producing oxygen by the alternate passage of air and steam over a hot reaction mass, in which large quantities of oxygen may be produced with a relatively small quantity of mass and a relatively low steam consumption. Another object is the provision of such a process whereby the stability of the reaction mass is improved. Still another object is the provision of such a process whereby oxygen may .be produced on a large scale with equipment of relatively small size requiring a relatively small initial investment. Still another object is the provision of such a process for producing oxygen from the fair at a relatively low cost. Another object is the provision of a novel process for reactivating an inactive contact mass.

The above and other objects, and the novel features of the invention, will become apparent from the following description of the process, having reference to the single ligure of the drawing, which is a flow sheet showing diagrammatically one form of apparatus for performing the process of the invention.

Fundamentally. the improvement of the present invention over the basic process of Du Motay et al. resides in the discovery that greatly improved yields of oxygen of high purity are obtained by maintaining the iiowing streams of air and steam at pressures above about two atmospheres absolute during their respective periods of passage-over the hot Contact mass. This is in marked: contrast-,1 to the processes of the prior art, in which the air and steam were at atmospheric pressure, or at most, at a low pres'- sure just sufficient to force the steam andA air through the mass. Moreover, pressure operation also improves the stability of the mass itself,- thuspermitting the same mass tobe kept in `per ation for a much longer time than was possible by prior known processes.

The oxygen production is directly proportional to the absolute atmospheres of steam pressure, so that any slight increase of steam pressure above one atmosphere "is beneficial. It is imprtant,fl however, f that the super-atmospheric pressure' at least'j be maintained throughoutV the massfor the best results,` and' that the pressure be substantially greater than is required merely tof force thesteam throughjthe mass, For practi'cal'purposesf'of course, the operating pressure should 'exceed' one atmosphereeby a substantial' amountf A t about` two atmospheres steam pres# sure Kabout `14.7"pounds perV squarel inch gauge), th'ej 'oxygen production is 'approximately twice thatat fone atmosphere under" otherwise identical conditions VV :Oneform of apparatussuitable for performing the process ofj the,4 invention is shown diagram` maticallyjin'the drawing.;` 1A' furnace F red by gasolinejorjanyotherf suitabljefuel, has two reaction"'vesselsRiV and Rainits interior, each orwhichisvchargedj with a quantityof a contact massvgsuch 4:a'sthe,alkali or alkaline earth metal Inanganate fniassfdi'sclosed 'and claimed'l in my'gc'operrdingapplication Serial No. 449,686', i'iled CQllfllrGIilY herewith? YAssuming[thatireactionvessel R1 is on the air phase' andlreaction' Vessel R'zis onj'the` steam phase, the operation proceeds as follows:I "Anf'airf compressor Af discharges 'air into a receiver LG, frornfrwhich itfpasses lby way of a conduitil toia-"T comprisingltwobranches i3 anldfnl 5.v The flow .Y ofj air through the Y branches Y I3 and I5 is"controlled by two inlet valve means I'I-an'd' I3, respectively, 'The'valve means l'I comprises two*interloclred valves; onev inj the branch conduitl I3 being open and the' other, in

a conduit 2 yl,`beingclosed. AThe valve means l 9 also comprises two interlocled valves, one in the branch-j conduit lsbeing closed and the other, in

a conduit 23', being open.

"Air-,Hows through'tlie branch conduit I3 to a conduit -25 leadin'gjtoa heat exchanger H1 arrangedfin'- the 'furnace F above the` vessel R1. From there the airfpasses'to a superheater S1 arranged, 'below the-vesseljRi, and is "thenrdischarged intof thev'esselRi where itlflows through the -porous Contactmass and is stripped of its oxygen; 4'The "hotj waste gas,` mainly` nitrogen, passes from the outlet of thel vessel R1 into .the heat exchangerI-Inin'whichit' flows countercurrently tothe incoming'air and helps to preheat i'lhef'latterlv Wasteg'as then passies'V by way ofY a'conduit 211tov'a branch condu it 29 of any--V other T; also includin'gfa branch conduit 3l.

llow o i` waste-` gas' through the Abranch conduits 29 and 3| is controlled by two outlet; valve means 33 and 35,. respectivelyt4 The; valve rneansf33- includes'two interlocke'd Valves, 'one Yin the branch conduit 29 being open and the other, in a coriduit 31, being closed. The valve means 35 also includes two interlocked valves, one in the branch conduit 3| being closed and the other, in a conduit 39, being open. As a result, the waste gas nows through the open conduit 29 into a Waste conduit 4I. and is discharged'v to thelatmosphere through a back pressure valve 43. l'f`idesired, the waste gas may be collected for use.

Meanwhile, a water pump P has been pumping water from, a water container W through a conduitlt into a steam coil or flash boiler B arranged in thef4 furnace F above the reaction vessels-- Ri and Rg.' rIhe Water is flashed to steam, which ows through a conduit `lll to another T,v comprising the two branch conduits 2l and 23.' Asthe` valve controlling the branch conduitj- 2l is closed, and that controlling the branch conduit 23 is open, the steam flows through theconduit 23v to a conduit; leading tfa 'secondhe'at exchanger H2v 'inL thef'fliiriagze, r1 abovthe v'esseinzffrhe preheated 's'.traz'arfn` from there passesI t0` a second'fsuperhea'ter and, theri'into 'the j'vessel Rfz, :where it 'passes tlriroughi theporus 'cht'actfmassaridi'zliberates gaseous Oxygen; ,1 A, Thev v'gaseous oxygen An iixed with residualVV steam leavesth 'vessel R'arld' passesv to the] heat 'exichangerHg, where it 'lowsjcountercurrently to ther entering steam, andhlps to preheatgthe latter, 'Er'omj there, the'V vsteam-oxygen 'mixture passes lcy'fway` of, a conduitfl to` the branch' conduit 33 voffanother"T,4 whiff?l also'.I includes the ibranchjcoriduift. `3'I,' through.' thev openv valve ofthe valvemeanslirand into aconduil '53(r Steamfih the 'Steam-oxygen mixture sndensed 'in' an aircooled condenser' C, thej hot' con# densate' and n 'onfconde'n sable'` gaseous oxygen thereafter passing intofthe top' o f thewater'cbntain'e'r W.y Gaseus oxygen then passes' to the suction sidev of an oxygen compressor O= which compresses the oxygen to "alhigh pressure, such as 2009 lbs/sq. in. The compressed oxygen is freed'of moisturein a rriisture trap "55, and in oneff a pai'ror'drying units D1- andl D2, whichj m'a'y' contain 4silica gel- 'o'r any other suitable" Water absorbing material. vThe highpressue dry gaseoiisA oxygen then 'flows through a back pressure valvel'l to" a charging racliiI E4 having connections forcharging thbxygn into cylinders or'the like.

After' tle'air Iand steam`reactions"have prof` ceededin the reaction vess'ls R21andRz,` respecl tivelygfoi apredetermineditervaljsucn a'sfiv" minutes-"the "flow of the",two'lfiuds is; inter-v eiiarfg'ed, 'Steam being thereafter passed throughtnfves'sei R11'f for cedric-iting the ebntictmassI and 'air' flowing thereafter' through the"y vessel R72" foroxidizir'g'l'theciitet rnaslsi'` fis accom#v plishedby jfl-r'st sirnii'ltaneouslyactuating'the two inletvalve "Irians Iflfarid l9f so 'v -hatthef'positions of the respective valvesfl reA reversed.; 'f" f" "Steam, fiorriuthe *stea coil" Bfwthen passesA thfoehfhe-blaehwrldu 2li tQ/hgondui., and l'theiice through the -heat exchanger H1 g and y the? `superheatferShintoy the'fvessel :3.1. At; the, Sa'r time. airffolm,therevr Grssesthrugh the* branch 'conduitL lltoftlie' conduit49,1 and, thme through the heat exchanger 'H2 :and the l Silllhfal Sz'nifheirefiionjvsel'Re Steam, entering the vessel. R1...drive$ ahead. 0f iti ll .reSQduafW-t. gas, which lis ,discharged 110,' the, aimes. 're' `tfiv'ug.YitlrlveWaste,wdwit 41- Tliehair enteringj the vesselA jRzpLdrives 'aheadj of it L alliV residual '.'steanif-,xygen niixture,` which 'passes to the 'conduitv 53.v VAfter a predetermined time lag interval for this purging operation, the two outlet valve means 33 and 35 are actuated to reverse the positions of the respective valves, and the cycle of operation is completed with the mass in Vessel R1 being deoxidized, and the mass in vessel R2 being oxidized. Steam-oxygen mixture from vessel R1 then is discharged through the branch conduit 3l to the conduit 53, and waste gas from vessel R2 is discharged through the conduit 3| to the waste conduit 4l.

After a predeterminedtime interval, such as five minutes, the whole cycle may be repeated by again actuating the valve means Il, I9, 33 and 35 to restore them to their original positions.

In the preferred form of the process of the invention, substantially equal air and steam pressures of at least about 75 pounds per square inch (gauge) are desirable. As the rate of oxygen production increases in direct proportion to the absolute atmospheres of steam pressure, at a steam pressure of about 75 pounds per square inch gauge (equal to about six atmospheres absolute) the rate of oxygen production for a given steam ow is approximately six times as great as it would be at atmospheric pressure under otherwise identical conditions with the same mass; and conversely, the quantity of steam required per unit volume of oxygen produced is about one sixth as great at 75 pounds per square inch as at atmospheric pressure with the same mass. As the result of pressure operation, therefore, it is possible to reduce Very materially the steam consumption per unit volume of oxygen produced, thus eiecting a heat balance between the steam and air requirements, a decrease in the size of equipment required, and a low cost of operation. The stability of the alkali manganate contact mass is also greatly improved as a result of operation under pressure.

The main reason that the air and steam are preferably maintained at substantially equal pressures is to prevent shocks to the mass when alternating between the air and steam phases of the process. However, theoretically the air pressure may be maintained much lower than the steam pressure without reducing the rate of oxygen production. In the two reversible reactions of the types of chemical systems involved in this process, one example being represented by the equation given above for the Du Motay et al. process, the oxygen production rate is controlled by the slowest reaction in the system. This slowest reaction is the deoxidizing reaction of the steam phase, and it is for this reason that large quantities of steam are required when operating at atmospheric pressure. The use of a super-atmospheric steam pressure speeds up the steam phase of the reaction and thereby increases the rate of oxygen production. It is well to note, moreover, that even when the air pressure is equal to the steam pressure, the partial pressure of oxygen over the contact mass is only about one-fifth of the total air pressure; and it is this partial pressure of oxygen over the mass which controls the rate of the reoxidation phase of the cycle.

The improvement of the present invention, namely, operation at super-atmospheric steam and air pressures, is not limited to any particular reaction mass. It greatly improves the rate of oxygen production and the stability of the mass when oxygen is produced by alternately passing air and steam over any suitable hot mass having the ability to be oxidized by the passage of air thereover, and thereafter to be deoxidized and Samples of this mass were subjected to a cycling operation consisting of alternate five-minute phases of air and steam, while the samples were maintained at a temperature of about 1200 F. Under these conditions, the yields of oxygen Vin cubic feet per hour for equal weights of mass and equal steam flows were as follows:

Oxygen Yield Cu. Ft. per

Operating Pressure Lbs. per Sq. In. Gauge Hour The process, using a mass as described above, was operated continuously for 25 days under pressure without any substantial deterioration of the mass.

A second example of the improved process was similarly performed, using a sodium manganate contact mass, prepared by first reducing manganese dioxide to an available oxygen content corresponding to Mn304, then mixing it with sodium hydroxide in the proportion of 2 mols of MnsO4 to 8 mols of NaOH corresponding theoretically to a compound having theoretically the formula 2Mn304-4Na2O, and sintering at about 2200 F. 'Ihe following yields of oxygen were obtained, expressed in cubic feet per hour for equal weights of mass:

Oxygen Yield Cu. Ft. per

Oxygen Yield Cu. Ft. per

Operating Pressure Lbs. per Sq. In. Gauge Hour The process of the invention also has been tested and proved advantageous on reaction masses containing alkali manganate plus silica up to 12% of the MnOz added. Moreover, the process is generally advantageous with masses containing chromium, manganese, lead, aluminum, molybdenum, and boron compounds, as well as with chromate and ferrate masses.

The rateof the steam phase `reaction .is also a function of the temperature, and has been Aobser-ved 4to increase approximately20% for an increase in temperature o f operation from l1150"-E. to 1300 F. However, it is the operation .of the process at super-atmospheric vpressures which constitutes the novel improvement of the vpresent-invention, regardless ofthe temperature used. The preferred temperaturelis about 1200'F., with steam and air pressures of -between about 75 and about 90 pounds per square inch gauge, when using -an alkali manganate contact mass.

When performingfthe process of producing oxygen described above, oxygen production tendsto stabilize at a constant rate which maybe above o r below the initial production rate, depending on the-nature of the contactnmass employed. fllhis constant yield rate is referred to as the stabilized yield level. When operation of the process proceeds normally, therate of oxygen production continues indefinitely at the stabilized level.

Due-to faulty operation, the activityof thecontact mass sometimes may be impaired to suenan extent that the oxygen yield is greatly reduced below the stabilized level. An excessive reduction in thesupply ofair may effect this undesirablel result, as may thenuse of excessive air ,pressures r ai;` flows onrsornetypes ofmasses. 1mpairment of the contact mass apparently results from disturbing the chemical equilibrium, which resultsin adepletion'inthe.amount of the active constituent present inthemass. ,Sodium mangliflatev (orptsum manganate) apparently is the-active ,constituent of the contact masses specifically described above.

When the activity of thecontactmass is so impaired vthat it loses some of itsability'totake .upV oxygen-during the Vpassage of air thereover, it may bereactivatedby .maintaining the mass in a hot condition Yand passing-aininto contact therewith at .condition-s of temperature andpres.- sure promoting the reformation of theV active constituents. Thismay be accomplishedby increasing the air pressure above the normal Operatingppressure by a substantial amount. Reactivation may be performed while retaining the Contact mass inV situ, thus avoiding the expense, time, and annoyance of removing the mas-s to a specialY reactivation apparatus.

It hasbeenfoundthat, when Va contactlmass having impaired activity is reduced internperature to belowllOG" F. and a flowing, streaml of air atsuper-atmospheric pressure is passed into contact'with the mass While maintaining the mass iny a hot reactive condition constantly below 1100 F., itsactivitywill be restored. VThepreferredtemperature for` reactivation. is 9,50*? 41?..,or lower,. and a, quantity of air ,slightlyY more, than that required, during .a Asingle operating cycle should be used. Also, it is desirable that the pressureof the air be somewhat higher than is used. during normal. operation. .When the, operating'temperature is again raised to at least 1100 F. and theair-steam cycle is resumed, the original stabilized level of oxygen production is obtained.

As an example of how reactivation is carried out, an impaired sodium manganate type contact mass was completely. reactivated by.A reducing. the temperature to- 950y F'. and. passingfairat :65 to 70 lbsi/sq. in.over` the Amass for 84 minutes. AUpon restoration of the original-operating temperatures'of-1200 F., andthe original steam and air pressures olf-60 lbs/sq. in., the original stabilized yield level was again obtained. Y

It is evident that the process of reactivating theeontavct mass may be performed while-raising or lowering vthe temperature of lthe mass to .place the unfit in operation, or on the completion of a run, or it maybe done as an interruption in the production procedure if the productive capacity hasvbecomeimpaired. Also, the reactivation proceduremay be vper-formed periodically to prevent the activity oflthe vmass from becoming too impaired. Furthermore, it is to be understoodthat the process of Yreactivation is applicable .to any contact-.mass having theability to be oxidized by the 4passage of air into contact therewith, and thereafter to be deoxidized and release oxygen by thepassage of steam thereover.

Although empiricalformulae and names have beengivento the masses to which this .process is applicable, .itis to b e understood that there is no evidencethat any or al1 of a particular mass has the exact formula. assignedto it. The masses are Yprepared by sintering together their constituentsiin thepropo-rtions vrequired theoretically to produce compounds of the indicated formulae, but the utlimate products may vary in While or in 'part from the ltheoretical formulae. This process, therefore, is not to be limited by any formulae ornames of chemicals used-herein.

I claim:

1. In fa process for extracting gaseous oxygen from a :nurture of Yoxygen with inert gas by alternatelypassing said mixture and steam in contact with a hot `manganate type contact mass, the stepsof maintaining said mass at a temperature of approximately l200F. whilemaintaining said mixture and said steam at approximately equal pressuresbetween approximately '75 and :approximately lbs/sq. in. gauge during the respective periods ofpassage of such mixture and such steam in Contact .withsaid mass.

2. In a process for extracting gaseous oxygen from a mixture oi oxygen with inert gas by alternately and successively passing said mixture and steamin contact with a hot solid contact mass having the .ability to absorb oxygen from such mixture andi-tovrelease the labsorbed oxygen during-the steam phasefsaid mass-comprising at least onesubstance selected from the group consisting of inanganates, chromates, and ferrates, the stepswhich Ycomprise maintaining said mass at atemperature Vbetween 1100 andlilQ F. and maintaining said-mixture and said steam at lappr-oximately equal pressures. above about two atmospheres absolute during-their respective periodsof passage.

3.'v In a process for extracting gaseous oxygen trema-mixture of oxygen with inert gas by alternat'elyJ-passing'said mixture andsteam in contact withahot manganatetype contact Ina-ss, the stepsy of maintaining said mass at a temperature betweenllOvQVrEkwand -1-300. F. While maintaining ysaid,.rnixture and said steamat Yapproximately equal pressures between v75- and '90 lbs/sq. in. gaugefduringetheirrespective periodsl of passage.

Y4. A process:forreactvating an impaired solid manganateltype -contact massY of the typenormally.' containing a substantial amountof anY active constituent comprising a manganate `com pound of an alkalrmetal, the Aamount of said manganate compound insaid mass havingfbeen so depleted `by thel -passageof steam and air at the operating temperature and pressure that said mass has lost some of itsability to take up oxygen duringithe passage of air, said Vlllrocesscomprisingllaintaining saidV mass a hot condition and passinaairirlt Gorilla@ therewith at pressure increased above said operating pressure tpro- 9 mote the reformation of said manganate compound.

5. A process for reactivating a manganate type contact mass impaired during the production of gaseous oxygen by the alternate passage of steam and air in contact therewith at super-atmospheric operating pressures and operating temperatures above 1100 F., said mass having lost some of its ability to take up oxygen during the passage of air thereover, said process comprising holding said mass at an elevated temperature constantly below 1100 F. and passing into contact therewith a owing stream of air at a pressure greater than said operating air pressure.

6. A process for producing gaseous oxygen which comprises alternately passing owing streams of air and steam at an operating temperature above 1100 F. and at super-atmospheric pressure in contact with a hot solid manganate type contact mass having the ability to be oxidized by the passage of air in contact therewith and thereafter to be deoxidized and release oxygen by the passage of steam in contact therewith; and, when the activity of said mass becomes so impaired that said mass loses some of its ability to take up oxygen during the passage of air, reactivating said mass by reducing the temperature thereof to below 1100 F. and passing into contact therewith a flowing stream of air at a pressure greater than said operating air pressure while holding said mass in a hot reactive condition constantly below 1100 F.

7. In a process for extracting gaseous oxygen from a mixture of oxygen with inert gas by alternately and successively passing said mixture and steam in contact with a hot solid manganate type contact mass having the ability to absorb oxygen from such mixture and to release the absorbed oxygen during the steam phase, the steps which comprise maintaining said mass at a temperature 10 between 1100 and 1300 F. and maintaining said mixture and said steam at approximately equal pressures above about two atmospheres absolute during their respective periods of passage.

8. A process for producing gaseous oxygen which comprises alternately passing owing streams of air and steam at approximately equal operating pressures above about two atmospheres absolute in contact with a hot solid manganate type contact mass maintained at a temperature between 1100 and 1300 F., said contact mass having the ability to be oxidized by the passage of air in Contact therewith and thereafter to be deoxidized and release oxygen by the passage of steam in contact therewith; and, when the activity of said mass becomes so impaired that said mass loses some of its ability to take up oxygen during the passage of air, reactivating said mass by maintaining said mass in a hot reactive condition and passing into contact therewith a ilowing stream of air at a pressure greater than said operating air pressure.

LESLIE G. JENNESS.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,124,304 Danckwardt Jan. 12, 1915 1,244,902 Scheller Oct, 30, 1917 1,848,723 Jaeger Mar. 8, 1932 1,015,556 Kaszner Jan. 23, 1912 FOREIGN PATENTS Number Country Date 487,785 Great Britain June 23, 1938 13,959 Great Britain 1895 3 034 Great Britain 1891 

